The goal of this project is to identify promising low-volume ventilation waveforms that will open occluded pulmonary airways with minimal damage to sensitive epithelial tissue. This problem is physiologically significant because the obstruction of pulmonary airways by a viscous liquid occlusion occurs in a variety of diseases including respiratory distress syndrome (RDS), acute respiratory distress syndrome (ARDS) and asthma. Airway closure contributes to mortality through ventilation-perfusion mismatch from reduced gas transport. In RDS and potentially ARDS, the lining fluid surface tension is elevated due to surfactant deficiency, which increases the pressure necessary to open the occluded airways. The proposed studies will test the hypothesis that pulsatile ventilation waveforms can be used to minimize damage to airway epithelial cells by maximizing surfactant transport and optimizing biophysical responses to reduce the damaging mechanical stress imparted on airway epithelium. Each specific aim couples computational simulations to laboratory experiments to elucidate the interactions between mechanical stresses, transport properties, surfactant biophysical responses and cell damage during the migration of a finger of air through a cylindrical tube as the model system. The specific aims of the project are: Specific Aim #1: Test the prediction that epithelial cells are wounded by the transient pressure gradient that sweeps across the cells during airway reopening and determine the stimulus/response behavior for steady and pulsatile flows. Specific Aim #2: Investigate the prediction that surfactant biophysical properties coupled to interfacial flow waveforms can protect the epithelium, and use the principles derived from these studies to predict properties of ventilation waveforms that will recruit an obstructed airway with minimal damage to the airway epithelium. Successful completion of this project will lead to improved understanding of the role of ventilation on lung injury. Improved ventilation protocols resulting from the principles derived from this study could lead to reduced mortality of infants and adults suffering from respiratory distress syndrome or asthma.